Critical Loads

Critical Loads as an internationally recognized standard

Are you an expert on air pollution, agriculture or nature conservation, dealing with the issue of nitrogen as an air pollutant, which can eutrophicate and acidify ecosystems?

Since no air pollution limit values for nitrogen or ammonia concentrations are contained in the Swiss air pollution control ordinance, Critical Loads can be used as an internationally recognized standard.

On behalf of the Swiss Federal Office for the Environment (FOEN), we provide basic information and calculation methods for the mapping of nitrogen and ammonia for Switzerland in a European context:

• CCE status report
• Nitrogen-containing airborne pollutants in Switzerland
• Ammonia emissions and nitrogen inputs

In many cantons similar plans are being worked on, or have already been developed. We would be happy to assist and advise you in the development of the basics and analysis.

Application for cantons and regions

Our experience from national projects can also be applied to cantonal and regional levels:

• Emission cadastres for Ammonia (NH₃) and Nitrogen Oxides (NO_X)
• Calculation and mapping of concentration distribution and deposition
• Determination of critical loads for nitrogen (CLN) in sensitive ecosystems using the UNECE methodology
• Mapping CLN excess and Critical Levels at the regional level and for single sources such as from farming facilities
• Calculation of scenarios and nitrogen balance
• Fundamentals for the planning of monitoring networks

The results are spatially resolved, validated and clearly presented in map by our powerful Geoinformatics business unit. Our Web & Software unit creates interactive map applications on the Internet or supports you in data management.

Determination of nitrogen load

The nitrogen deposits from the atmosphere can lead to undesirable fertilising and acidification effects in ecosystems, such as forests, high and lowland marshes, dry meadows and pastures. In consideration of these effects, the concept of Critical Loads is applied within the framework of the UNECE Convention on Long-Range Transboundary Air Pollution (LRTAP).

For modeling we consider the following chemical N-components: ammonia, ammonium, nitrogen dioxide, nitrate and nitric acid.

One possible application of a nitrogen deposition map is the determination of Critical Load exceedances.

Dispersion model for ammonia immissions

95% of gaseous ammonia emissions originate from agricultural activities such as livestock farming, as well as the storage and spreading of manure and dung.

For the calculation of ammonia emissions we use the dispersion model Agrammon. With conversion functions the ammonia emissions are converted into ammonia immissions. Our Geoinformatics business unit is tasked with the implementation and visualisation.

On behalf of the Swiss Federal Office for the Environment (FOEN), the spatial distribution of the various sources was determined from Swiss emissions using area statistics and agricultural plant surveys.